1. Field of the Invention
The present invention relates to a load/unload-type head suspension for supporting a slider of a disk drive incorporated in an information processor such as a personal computer.
2. Description of Related Art
A hard disk drive (HDD) such as a magnetic disk drive employs hard disks that are rotated at high speed. On each rotating hard disk, a slider attached to a head of a head suspension is slightly floated to write and read data to and from the hard disk through a transducer incorporated in the slider. The head with the slider is supported with the head suspension so that the slider may be slightly raised from the hard disk.
When stopping the disks, the magnetic disk drive must retract the slider from recording tracks of the hard disk. For this, there are two known methods, i.e., a contact start/stop (CSS) method and a load/unload (LUL) method.
The CSS method moves, when the hard disk is stopped, a front end of the head suspension to a CSS area prepared along an inner circumference of the hard disk. To avoid the slider from being attracted to the surface of the stopped hard disk, the surface of the CSS area of the hard disk is slightly roughened. The CSS area, therefore, is not usable as a recording area, to decrease a recording capacity. Increasing a recording capacity may be achieved by lowering the fly height of the slider. The roughened surface of the CSS area of the hard disk, however, prevents the lowering of the fly height.
The LUL method is also called a ramp load method. A ramp block made of synthetic resin is arranged at a side of the hard disk. When the hard disk is stopped, the head suspension is moved to a retract position. At this time, a tab (load bar, ramp contact, or corner) formed at a front end of the head is slid and guided along a slope of the ramp block so that the slider may be separated away from the hard disk.
The LUL method is capable of preventing the slider and the hard disk from being damaged even if a shock or vibration is applied to the disk drive while the disk drive is being carried. The LUL method allows the surface of the hard disk to be uniformly smoothed to the maximum, to thereby lower the fly height, open the inner circumferential area of the hard disk for data recording, and increase the recording capacity. During the use of the computer, the hard disk drive can be safely stopped if it is not used, to save electricity.
For the LUL method, an unload operation of the head suspension must be carried out smoothly. For this, an important factor is the magnitude of unload force (UL force) “f” acting on the tab during the unload operation.
FIG. 24 is a view explaining force acting on the tab when the tab is slid and guided along a ramp block. In FIG. 24, the tab 101 climbs a slope 105 of the ramp block 103. At this time, the tab 101 receives unload force f, vertical reaction N due to load F that presses the tab 101 to the ramp block 103, and frictional force μN along the slope 105 based on a frictional coefficient, between the tab 101 and the ramp block 103.
If the slope 105 has an inclination angle of θ, a ratio α between the load F and the unload force f is expressed as follows:
  α  =            f      /      F        =                  (                              sin            ⁢                                                  ⁢            θ                    +                      μ            ⁢                                                  ⁢            cos            ⁢                                                  ⁢            θ                          )            /              (                              cos            ⁢                                                  ⁢            θ                    -                      μ            ⁢                                                  ⁢            sin            ⁢                                                  ⁢            θ                          )            
This expression indicates that the unload force f is dependent on the inclination angle θ, load F, and frictional coefficient μ.
FIG. 25 is a graph showing relationships among frictional coefficients, inclination angles, and unload force.
To expand the recording area of a hard disk, the disk must be used up to the outer circumference thereof within a limited space of the hard disk drive. In the limited space of the hard disk drive, the slider must be raised from the hard disk and moved to a retract position of the ramp block with a shortest moving distance. For such a shortest-distance unload operation, it is advantageous to increase the inclination angle θ of the ramp block 103. However, as is apparent in FIG. 25, the unload force f nonlinearly increases when the inclination angle θ exceeds about 25°. Accordingly, the inclination angle θ is usually set in the range of 15° to 25°. Dimple load of the head suspension must be high in consideration of a shock to be applied during the carrying of the hard disk drive. Generally, an upper limit of the dimple load is 3 gf, and the load F is lower than that. The smaller the frictional coefficient, the better.
FIG. 26 is a graph showing results of calculations of the unload force f with respect to various frictional coefficients. The calculations were made with a standard dimple load of 3 gf, an inclination angle θ of 18.5°, a load F of 2.3 gf, and a spring constant k of the tab 101 of 1.9 gf/mm.
In FIG. 26, a rightward-increasing part on the left side of each curve indicates that the tab 101 is climbing the slope 105. After the slope 105, the unload force f sharply decreases to a magnitude that is dependent only on a frictional coefficient. FIG. 26 shows that the unload force f is greatly dependent on the frictional coefficient. When the frictional coefficient changes from 0.1 to 0.3, the unload force f increases 1.5 times from 1 gf to 1.5 gf. This means that, in a magnetic disk drive having four head suspensions, the unload force f increases from 4 gf to 6 gf. In this way, the smooth unloading of the head suspension will be hindered if the frictional coefficient varies.
In the load/unload-type head suspension, the frictional coefficient of the tab 101 must be reduced, and in addition, variations in the frictional coefficient must be minimized (refer to, for example, Japanese Unexamined Patent Application Publication No. Hei-11-96527).